Japanese Laid-Open Patent Publication No. 2003-127928 discloses a circuit structure including a flasher switch (winker switch) and a hazard switch, which are connected between a flasher controller (controller) and ground. The winker switch and the hazard switch are connected in parallel. Since the winker switch and the hazard switch are connected in parallel, they can be connected to the controller using the same wires (harnesses), thereby reducing the number of harnesses.
In recent years, lighting devices (lighting bodies) including light-emitting diodes (hereinafter also referred to as “LEDs”) as light sources have been developed for device downsizing and reduced power consumption. If a winker switch and a hazard switch are connected in parallel between a controller and ground in combination with an LED lighting body that can be energized with a low current, as disclosed in Japanese Laid-Open Patent Publication No. 2003-127928, then when a leakage current flows in the winker switch and/or the hazard switch, the LED may possibly be turned on erroneously by the leakage current.
For the above reasons, it has been desirable for a lighting control system on a vehicle to control a lighting body to blink only after the lighting control system has determined that the driver of the vehicle has turned on a winker switch or a hazard switch. One circuit arrangement proposed for such a lighting control system includes a winker switch and a hazard switch, which are connected as high-side switches between a controller and a power supply. The controller determines that the winker switch and the hazard switch have been turned on by detecting an input voltage, which is applied from the power supply when the switches are turned on.